Keen local historian Jon Gunson has compiled this series entitled Friday Knight - knights who fought at the Battle of Lewes - giving each a brief biography.
Sir Roger held Mitford Castle in Northumberland ( N.b. perhaps the only five-sided Great Tower in England). When Northampton Castle fell to the King’s army on April 5th, 1264, he was taken prisoner, and entrusted to Sir William de Valence. He was released in time to fight for de Montfort again at Lewes, on 14th May. (I wonder if a ransom comes into this somewhere. It usually did). He was summoned to Parliament on 24th December of the same year.